Metabolism of cyclophosphamide by rat hepatic microsomes.
Metabolism of cyclophosphamide by rat hepatic microsomes.
复制标题
大鼠肝微粒体对环磷酰胺的代谢。
作者：
N. Sládek
总结表征了从雄性大鼠肝脏获得的微粒体将环磷酰胺转化为其烷基化代谢产物。在所用条件下，发现反应（a）是温度依赖性的;（B）是酶浓度依赖性的;（c）以线性方式进行20分钟;（d）定位于肝微粒体部分（在步行者256癌肉瘤细胞组分或胸腺、肾上腺和肾细胞组分中未发现活性）;（e）需要NADPH（NADH不能作为电子供体）;（f）被一氧化碳抑制;（g）被烟酰胺非竞争性抑制;（h）如果使用先前冷冻的而不是新鲜的微粒体，则会受到极大抑制。环磷酰胺结合微粒体血红素蛋白引起的I型谱。根据Lineweaver-Burk图测定，Vmax为4.20 μ mol/g/hr，Km为1.39 mm。雌性大鼠和小鼠肝脏微粒体代谢环磷酰胺的Vmax分别为0.66和9.69 μ mol/g/hr，Km分别为0.67和0.68 mm。环磷酰胺竞争性抑制乙基吗啡的代谢，反之亦然。当每个Ki 9用作其他9代谢的抑制剂时，Ki 9等于它们各自的Km 9。这些研究结果和2-底物动力学研究支持的结论是，相同的酶系统或系统的共同限速步骤催化环磷酰胺，乙基吗啡，和许多其他药物在大鼠肝脏的生物转化。虽然在体外观察到雄性和雌性大鼠之间代谢速率存在较大差异，但通过单次腹腔注射环磷酰胺后的血液烷化剂活性水平估计，在体内未发现比例差异。
Summary The conversion of cyclophosphamide to its alkylating metabolite(s) by microsomes obtained from male rat liver was characterized. Under the conditions used, the reaction was found (a) to be temperature dependent; (b) to be enzyme concentration dependent; (c) to proceed in a linear fashion for 20 min; (d) to be localized to the hepatic microsomal fraction (no activity was found in Walker 256 carcinosarcoma cell fractions or in thymus, adrenal, and kidney cell fractions); (e) to require NADPH (NADH could not serve as an electron donor); (f) to be inhibited by carbon monoxide; (g) to be inhibited noncompetitively by nicotinamide; and (h) to be greatly depressed if previously frozen rather than fresh microsomes were used. Cyclophosphamide bound to microsomal hemoprotein elicited a Type I spectrum. As determined by a Lineweaver-Burk plot, the Vmax was 4.20 µmoles/g/hr and the Km was 1.39 mm. Microsomes from livers of female rats and mice metabolized cyclophosphamide with a Vmax of 0.66 and 9.69 µmoles/g/hr, respectively, and a Km of 0.67 and 0.68 mm, respectively. Cyclophosphamide inhibited metabolism of ethylmorphine competively and vice versa. The Ki9s when each was used as an inhibitor for the other9s metabolism equaled their respective Km9s. These findings and 2-substrate kinetic studies support the conclusion that the same enzyme system or systems with a common rate-limiting step catalyze the biotransformation of cyclophosphamide, ethylmorphine, and many other drugs in rat liver. While large differences in rates of metabolism were observed in vitro between male and female rats, proportional differences were not found in vivo as estimated by blood levels of alkylating activity following a single injection of cyclophosphamide i.p.